Crystalline fructose is commercially manufactured by a very involved and time-consuming crystallization process which requires relatively sophisticated processing machinery and apparatus and careful control of process conditions, to ensure the production of a satisfactory crystalline-fructose product. As is well known, anhydrous fructose crystals may be obtained by crystallization of the fructose from both aqueous solutions and aqueous alcohol solutions, such as aqueous methanol and aqueous ethanol solutions of fructose. The employment of solvents in fructose solutions is undesirable, both from the economic point of view and since the resulting crystals precipitated from the solution and the liquid containing the solvent must have the solvent completely removed prior to consumption or use of the crystalline fructose, while economic operations also dictate the removal of the solvent from the mother liquid for use in the process.
A number of processes have been proposed in connection with the production of crystalline fructose from aqueous solutions. However, none of said processes has been satisfactory wholly, since they involve a number and a variety of process steps and careful control of various process-operating conditions and typically result in only very low yields of crystalline fructose.
For example, as disclosed in U.S. Pat. No. 3,513,023, crystalline fructose is produced through the employment of a fructose solution having at least 95% by weight fructose concentration, which is further concentrated in a vacuum to a water content of from about 2% to 5% and then cooled to a temperature of from about 60.degree. F. to 80.degree. F. A large quantity of the crystals are then added to the concentrated, cooled solution, and the mixture then must be stirred at a low temperature until it becomes a soft mass. This mass then is made solid and is dried at a temperature below about 150.degree. F. The proposed process is not satisfactory where it is essential to the process that the fructose concentration be not less than 95%, that kneading of the soft mass occur and further that only pure crystalline fructose seed crystals be employed. The proposed method thus has disadvantages both in terms of material handling and high-energy costs, as well as being limited to the employment of pure fructose syrups.
Another fructose process is described in U.S. Pat. No. 3,883,365, which is directed to the process of the production of crystalline fructose from an aqueous solution, and which process involves providing a saturated fructose solution, adjusting the pH of the saturated solution within a pH of 4.5 to 5.5, and then seeding the solution with fructose crystals, and, thereafter, lowering the temperature of the solution and optimally evaporating the solution to cause the formation of crystalline fructose. The resulting crystalline fructose is then separated by centrifuge methods. This process requires a very careful controlled-temperature cooling of the over 90% fructose solution to generate crystals and to increase the crystal size. Seed crystals must be pure fructose crystals of low crystalline size, and the yield produced is typically less than about 50%. Periodically, the process must be stopped and the solution, from which crystallization is being carried out, diluted with additional water, to avoid supersaturation levels of the solution. The essence of the invention involves a criticality of the pH and the need to adjust the pH to the range of 4.5 to 5.5.
A further method for obtaining anhydrous fructose crystals is set forth in U.S. Pat. No. 3,928,062, which is somewhat similar to the process described in U.S. Pat. No. 3,883,365, wherein crystalline fructose is produced from a supersaturated fructose solution, seeding anhydrous crystals into the solution and then concentrating and/or coating the solution while maintaining the sugar concentration and the temperature in the liquid phase within a carefully defined range, and then recovering the anhydrous crystals from the mass. Once again, the yield is typically under 60%, while the disadvantages of the process also require precise control of process variables, such as the rate of cooling and the rate of evaporating, and the syrup concentration is limited to less than 90% by weight, in order to avoid supersaturated solutions.
A further process is also described in U.S. Pat. No. 3,929,503, wherein a method is provided to obtain free-flowing anhydrous particles of glucose, fructose or mixtures thereof in such forms as powder, pellets, granules and the like, without subjecting the solution to a crystallization step. The process involves kneading of crystals or powder of anhydrous glucose, fructose or mixtures thereof; that is, a mother powder, with a syrup containing 40% to 90% of the same type of sugar as the mother powder, so that the resulting mixture forms wet particles having a moisture content of less than about 7%. The disadvantage of this particular process is that, even in the case of the most favorable concentration of 95%, it is recognized that it is very difficult to distribute uniformly the powder, due to the practical difficulties of admixture, such as, for example, the very high viscosity. Once again the yield is only about 54%, as the remaining material must be recycled as the mother powder, and both energy costs and material-handling costs are much higher, because of the poor yield.
Therefore, it would be most desirable to provide a process for the production of crystalline fructose, which process avoids the many disadvantages of the prior-art processes, and which process would present a simple and economical process avoiding the large capital and equipment costs and the careful process-control conditions associated with the prior-art processes.